fix: base open-discovery repo warning on unique repos

[hera8939]

Summary

Closes #972.

Fixes the Miner Details open-discovery repo-limit warning so it is based on the number of unique repositories eligible for scanning, not the raw PR count.

The scan helper already de-duplicates PRs by repository before applying the 50-repository cap. The UI warning now uses that same uncapped unique repository count, so miners with many PRs in a small number of repositories no longer see a false repo-limit warning.

Changes

• Add selectMinerIssueScanRepoSummary() to return both capped scan repos and uncapped unique repository count.
• Keep selectMinerIssueScanRepos() as the existing capped-list API.
• Update MinerOpenDiscoveryIssuesByRepo to show the repo-limit warning only when unique repositories exceed the fetch limit.
• Add regression tests for many PRs in few repos and more than 50 unique repos.

Testing

npm test -- --run src/tests/useMinerRepositoriesOpenIssues.test.ts
npx prettier --check src/hooks/useMinerRepositoriesOpenIssues.ts src/components/miners/MinerOpenDiscoveryIssuesByRepo.tsx src/tests/useMinerRepositoriesOpenIssues.test.ts
npx eslint src/hooks/useMinerRepositoriesOpenIssues.ts src/components/miners/MinerOpenDiscoveryIssuesByRepo.tsx src/tests/useMinerRepositoriesOpenIssues.test.ts --ext ts,tsx --max-warnings 0
npm run build